1. Field of the Invention
The invention relates to an encoding system conversion apparatus and a method for encoding system conversion, which converts video data of an arbitrary encoding system to video data of a different encoding system.
2. Description of Related Art
Advancements in recent years in digital signal processing technology have made it possible to perform highly efficient encoding of large amounts of digital information, such as digital data of moving images, still images, and audio. Applying such technology, development is underway of imaging apparatuses enabling the easy capture of high-quality images and quick output of the images to a recording medium.
At present, in many moving image capturing devices, a magnetic tape recording medium is used to record the encoded image data. The performance of read-write CDs (Compact Discs) and the like which are capable of reading and writing encoded image data is improving, and rapid development of imaging equipment using disk recording media.
Although a disk recording medium has better random access than tape recording medium, it has much smaller storage capacity than tape recording media. For this reason, imaging equipment using a disk recording medium generally uses an encoding system that has a better compression ratio than those used in imaging equipment using tape media.
Given the above-noted situation, in order to store encoded image data that is stored on a tape recording medium onto a disk recording medium, there is a need, not merely to copy the encoded image data, but to convert the encoded image data to an encoding system having a better compression ratio. To achieve this conversion from an encoding system with a low compression ratio to an encoding system with a higher compression ratio, an encoding system conversion apparatus is used.
FIG. 1 of the accompanying drawings is a general block diagram of an encoding system conversion apparatus of the past.
The encoding system conversion apparatus 900 shown in FIG. 1 has a function of converting a first encoded image data encoded in a first encoding system to a second encoded image data encoded in a second encoding system.
The first recording medium 901 shown in FIG. 1 stores the first encoded image data encoded by the first encoding system. The decoding section 902 decodes the first encoded image data encoded in the first encoding system to obtain an image signal and outputs the resulting image signal. The decoding section 903 encodes the image signal decoded by the decoding section 902 by the second encoding system and generates the second encoded image data. The second recording medium 904 records the second encoded image data generated by the decoding section 903.
The first recording medium 901 is a tape recording medium and the first encoding system is an encoding system using intra-frame encoding only. The second recording medium is a disk recording medium and the second encoding system is an encoding system using inter-frame encoding. In this system, the compression ratio of the second encoding system is greater than the compression ratio of the first encoding system.
The processing performed in the encoding system conversion apparatus configured as noted above is as follows.
First, the decoding section 902 reads out the first encoded image data encoded by the first encoding system from the first recording medium 901, decodes the encoded image data to a image signal, and outputs the decoded image signal to the encoding section 903. Next, the encoding section 903 encodes the image signal output by the decoding section 902 by the second encoding system, generates the encoded image data, and records the generated data onto the second recording medium 904.
By the above operations, the encoding system conversion apparatus 900 converts the first encoded image data stored on the recording medium 901 to the second encoded image data and stores the second encoded image data on the second recording medium 904.
In the above-described example, because after first decoding the already encoded image data to a image signal, a completely new encoding is performed using a different encoding system, there is the problem of a great deterioration in image quality at the time of conversion. There exists known technology to solve this problem by reducing the image quality deterioration by integrating the decoding section and the encoding section, and performing encoding by the second encoding system without completely decoding the first encoded image data.
The above-noted prior art, however, still had the problem of an insufficient effect in the case in which there is a great difference between the target second encoding system and the first encoding system. Additionally, there is a known method of making a number of trial encodings using the second encoding system, estimating the data amount distribution from the result of the first encoding, and performing re-encoding based on this result. Although this method is very effective in limiting image quality deterioration, it has the problem of requiring a very long processing time, because of the increase in the number of encodings.